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LIQUID CRYSTALLINE COMPOUNDS IN PYRIDINE SERIES
A. Pavluchenko, N. Smirnova, E. Kovshev, V. Titov
To cite this version:
A. Pavluchenko, N. Smirnova, E. Kovshev, V. Titov. LIQUID CRYSTALLINE COM- POUNDS IN PYRIDINE SERIES. Journal de Physique Colloques, 1979, 40 (C3), pp.C3-1-C3-4.
�10.1051/jphyscol:1979301�. �jpa-00218691�
JOURNAL DE PHYSIQUE Colloque C3, supplt2ment UU no 4, Tome 40, Avril 1979, page C3-1
S YNTHESlS AND CHEMICAL A PPL ICA TIONS.
LIQUID CRYSTALLINE COMPOUNDS IN PYRIDINE SERIES
A. I. PAVLUCHENKO, N. I. SMIRNOVA, E. I. KOVSHEV and V. V. TITOV Organic Intermediates & Dyes Institute, Moscow K-1, U.S.S.R.
R6sum6. - Des alkoxy-5 picolinates et alkoxy-6 nicotinates de phknyle substitub en para ont kt6 synthetises. Les relations entre leurs temperatures de transition, leurs constantes diklectriques et la position de I'htttroatome et la nature du groupement central ont ete Ctudiees et comparCes avec les donnees connues pour les derives benzeniques analogues. Un abaissement sensible des tempkratures de fusion et de transition isotropique a CtC observe dans le cas des pyridines substituees en b8ta.
Les stabilitks thermiques des derives alpha ne changent que trks peu.
Abstract. - Series of liquid crystalline 4-substituted phenyl 5-alkoxypicolinates and 6-alkoxyni- cotinates were prepared, and dependences of the phase transition temperatures and the dielectric properties upon the position of the heteroatom and the nature of the central linkage were investigated.
The data obtained were compared with those for related benzene derivatives. A noticeable lowering of both melting and clearing points was observed for P-substituted pyridines. In the case of cc-substi- tuted pyridines the mesophase thermal stability changes insignificantly.
1. Introduction. - Up to now there is no systematic study of liquid crystalline pyridine derivatives, although several papers on some Schiff bases [I, 21 and terphenyl heteroanalogues [3, 4, 51 have been appeared previously. This fact is apparently due to a difficult access to pyridine analogues of benzenic liquid crystals. Meanwhile a substitution of a benze- nic ring by pyridinic one allows to extend considerably the classes of potentially mesomorphic compounds.
Furthermore it appears to be supplementary possi- bilities to modify a direction and a magnitude of a dipole moment and by the same a sign and a magni- tude of a dielectric anisotropy of liquid crystals. This paper is a part of our investigations on the synthesis and properties of pyridine analogues of well known benzenic liquid crystals.
2. Experimental. - Transition temperatures were measured using a MIN-8 polarizing microscope fitted with a Mettler FP-52 heating stage and FP-5 control unit. Satisfactory elemental analyses were obtained for all compounds. Intermediate 5-alkoxypicolinic and 6-alkoxynicotinic acids were described by us earlier [6].
Para substituted phenyl 5-alkoxypicolinates (I) and 6-alkoxynicotinates (11) were obtained by reaction of the appropriate acid chlorides with para substituted phenols in benzene in the presence of triethylamine.
All pyridine containing esters were purified by chro- matography on the alumina with a following crystalli- zation from an appropriate solvent.
Azo-compounds (111) were synthesized by conden- sation of diazotized p-aminobenzonitrile with 3-
hydroxypyridine with subsequent alkylation or acyla- tion of intermediate 2-p-cyanophenylazo-5-hydro- xypyridine.
3. Results and discussion. - Transition tempera- tures of compounds 1-111 are listed in tables 1-111 respectively. As it follows from tables I and I1 and figures 1 , 2, the compounds I1 where R2 is alkyl or alkoxy group (IIa-f) have 20-30° lower melting points and 30-40° lower clearing points than those of appropriate p-substituted phenyl p'-alkoxybenzoates (IV) whereas similar compounds Ib-g have approxi- mately the same order of transition temperatures as compounds IV.
In the case of esters where R2 is cyan0 group, the clearing points are more sensible to the replacement of benzenic ring by pyridinic one and a difference makes up 10-30° for compounds Ih-j and 30-50°
for compounds IIg-i.
Thus, mesomorphic properties of non-conjugated two-ring compounds (benzenic and pyridinic rings are linked by ester group) depend not only on the molecule symmetry (position of a hetero-atome in this case) but also on the more complex interaction between a heteroatom and a terminal group (R2) in the benzenic ring.
In the case when the both pyridinic and benzenic ring in the mesomorphic molecule are conjugated (compounds IIIa-d, Table 111) a certain increase of a mesophase thermal stability accompanied by consi- derable rise of melting points are observed as expected (in comparison with benzene isologues IV).
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979301
C3-2 A. I. PAVLUCHENKO, N. I. SMIRNOVA, E. I. KOVSHEV AND V. V. TITOV
Com- pound
index
-
Ia b
C
d e f g h
1
j k 1
Para-substitutedphenyl5-alkoxypicolinates (I)
Yield
%
-
54 56 39 46 52 74 49 32 38 46 5 1 5 3
C-N,
OC (C-S)-
57.4 (*) 68.9 56.7 60.7 (*) 54.7 (60.7)
70.2 85.4 (*) 67.8 72.3 (*) 123.5 108.5
N-I, OC - 33.6 83.1 80.7 58.4 85.8 85.2 77.5 66.6 72.0 71.2 159.0 160.2
AC-N
-
-
+
4.4+
0.2+
15.7- 9.8
- 6.3
+
1.7- 1.6 - 2.7
+
0.7-
- 4.8
AN-I
- -
- 8.4
- 4.8
- 0.6
- 4.2 - 1.8
- 8.0 - 29.4
- 9.0
- 10.8
-
- 19.0
(*) Monotropic transition. AC-N and AN-I differences of transition temperature with those of benzene analogues (also in the Tables I1 and 111).
Com- pound index
-
IIa b
C
d e f g h
1
j k 1
Yield
%
-
61 60 58 72 70 71 65 60 62 59 71 70
C-N, OC (C-S)
-
45.8 47.4 (*) 46.2 (*) 33.5 (*) 42.3 45.5 84.3 (*) 61.3 (*) 88.2 (*) 80.6 (82.8) (77.6)
AC-N
-
- 18.7 - 21.1 - 10.3 - 11.5 - 22.2 - 21.5 - 2.7 - 9.2 - 3.8
+
9.0-
- 13.2
AN-I
- - 43.7
- 45.9
- 40.8 - 40.0
- 37.8 - 36.0
- 51.7
- 26.5
- 53.5
-
LIQUID CRYSTALLINE COMPOUNDS IN PYRIDINE SERIES
Compound
index R C-N, OC N-I, O C AC-N AN-I
- - - - - -
IIIa C ~ H I ICO 121.8 116.5
+
55.4+
6.0b C6H I ~ C O 112.6 111.3 f 46.3
+
6.7c C4H9 140.9 138.9
+
75.5+
12.1d 111.3 132.2
+
42.6+
15.9FIG. 1. - Influence of a heteroatome position on transition tem- peratures of p-cyanophenyl alkoxypyridinecarboxylates :
RO+O+N - (3 C-N transition
x N-I transltlon
A replacement of benzenic ring by pyridinic one affects also dielectric properties of mesogenes that can be used in the search of electrooptical composi- tions taking into account a simultaneous lowering of a solid-nematic transition temperature. Typical values of dielectric anisotropies of compounds 1-11 are listed in the table IV.
Acknowledgment. - We wish to thank Dr. M. F.
Grebenkin for measurements of dielectric constants.
FIG. 2. - Influence of a heteroatome position on transition tempe- ratures of p-hexyloxyphenyl alkoxypyridinecarboxylates :
R4=!-C00*c6H
1 3 - (3 C-N transition R+o+6H13 - - - x N-I transitionTABLE IV
Dielectric properties of esters I and I1 at T = T N - , - 10 OC Compound
index 11
EL A&
- -
Ib 5.60 5.85 - 0.25
h 33.8 16.6
+
17.2IIe 3.40 4.30 - 0.90
f 3.45 4.25 - 0.80
k 12.0 7.0
+
5.0A. I. PAVLUCHENKO, N. I. SMIRNOVA, E. I. KOVSHEV AND V. V. TITOV
References
[I] CHAMPA, D. A,, Mol. Cryst. Liq. Cryst. 19 (1973) 233. [ S ] SCHUBERT, H., WISS, Z., Univ. Halle, XIX, 70M, H5, S1.
[Z] YOUNG, W. R., HALLER, J., WILLIAMS, L., Liq. Crystals and [6] PAVLUCHENKO, A. I., SMIRNOVA, N. I., TITOV, V. V., KOVSCHEV, Ordered Fluids (Plenum Press, New York) 1970 383. E. I., DJUMAEV, K. M., Mol. Cryst. Liq. Cryst. 37 (1976) [3] SCHUBERT, H., ZASCHKE, H., J. Prakt. Clzein. 312 (1970) 494. 35.
[4] NASH, J. A., GRAY, G. W., Mol. Cryst. Liq. Cryst. 25 (1974) [7] DEMUS, D., DEMUS, H., ZASCHKE, H., Fliissige Kristalle in
299. Tabellen, Leipzig, 1974.
